An electric halogen incandescent lamp of this type is known from DE 3827451. Besides iron oxide, the known light-absorbing coating further comprises titanium oxide, manganese oxide and magnetite, FeO4, as pigments and, before being burned onto the glass of the lamp vessel, ethyl silicate as an adhesive. The known coating is obtained from a suspension which additionally comprises sodium metaphosphate, glycol, monobutyl glycol ether, and ethanol. The suspension has a relatively complicated composition. The known suspension has the disadvantage of a relatively short shelf life of about 3 days, and when burned onto the lamp vessel and being converted into the light-absorbing coating, this light-absorbing coating can be knocked off the lamp vessel comparatively easily. Furthermore, the manganese oxide often comprises lead (oxide) as a contaminant and is therefore relatively harmful to the environment.
An electric lamp is known from GB 1422491 which has a light-absorbing coating of approximately one-third by weight of glass frit comprising more than 70% by weight of lead oxide, and in addition silicon oxide and boron oxide, as well as the oxides of iron, cobalt and manganese as pigments. It was found that this coating adheres permanently to a lamp vessel made of hard glass, i.e. aluminosilicate glass or borosilicate glass, for example, having a coefficient of thermal expansion in the range of 3*10−6<=coeff. of thermal exp.<=7*10−6, but it quickly starts flaking off glass with an SiO2 content of at least 96% by weight, such as quartz glass, which has a much lower coefficient of thermal expansion than hard glass. Another disadvantage is that this coating comprises substances which are harmful to the environment: cobalt oxide in the pigment and lead oxide in the glass frit. This coating has the further disadvantage that it transmits comparatively much light. This disadvantage becomes proportionally more aggravating as the luminance of the light source is higher, as is the case with, for example, a high-pressure discharge lamp. Such a high-pressure discharge lamp suitable for use as a vehicle headlamp is described in EP 708978. The light-absorbing coating of the lamp disclosed in this document is obtained from, for example, a suspension comprising only silicon powder and iron powder, which is described in patent DE 2837280.